Digestion System &
Nutrition
By: Kreauna Bonner, Shalana Hunter,
and Jazelle Jackson
http://www.studyblue.com/notes/note/n/nutrition-final/deck/4816060
What is Digestion?
 Digestion: Is
the chemical and mechanical
break down of food and the absorption of the
resulting nutrients by cells.
 Mechanical Digestion: Breaks large pieces into
smaller ones without altering their chemical
composition.
 Chemical Digestion: Breaks food into simpler
chemicals
The Digestive System
The digestive system consists of the alimentary
canal.
 The alimentary canal extends about 8 meters
from the mouth to the anus, and several
accessory organs that secrete substances used
in the process of digestion into the canal.
The Digestion System
The Alimentary canal includes:
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Rectum
 Anus
Accessory organs include:
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Salivary glands
 Liver
 Gallbladder
 Pancreas
Alimentary Canal
The alimentary canal consists of four distinct layers that are developed
to different degrees from region to region.
These layers are:
 Mucosa (mucous membrane): surface epithelium, underlying
connective tissue, and a small amount of smooth muscle form this
layer
 Submucosa: consists of considerable loose connective tissue as well
as glands, blood vessels, lymphatic vessels, and nerves organized
into a network called a plexus.
 Muscular layer: produces movements of the tube
 Serosa (serous layer): The visceral peritoneum comprises the serous
layer, or outer covering, of the tube.
Movements of the Tube
The motor functions of the alimentary canal are of two basic types:
Mixing Movements and Propelling Movements
Mixing occurs when smooth muscles in small sections of the tube
contract rhythmically
 Example: When your stomach is full, waves of muscular
contractions move along its walls from one end to the other.
Propelling includes a wavelike motion called peristalsis.
 Peristalsis occurs when a ring of contraction appears in the wall of
the tube, while this happens the muscular wall just ahead the rings
relaxes
 When the peristalsis waves move along, it will push the tubular
contents ahead of it
Tube Movement
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Mixing movements
occur when small
segments of the
muscular wall of the
alimentary canal
contract rapidly
 Peristalic waves
move the contents
along the canal
Mouth
The Mouth
It receives food and begins mechanically reducing the size of
solids and mixing them with saliva.
The lips, cheeks, tongue, and palate surround the mouth to help
with the breakdown of food.
Cheeks and Lips
The cheeks consist of outer layer of skin, pads of hypodermic fat,
muscles associated with the expression of chewing, and inner
layers of moist stratified squamous epithelium.
The lips are very highly mobile structures. They consists of
skeletal muscles and sensory receptors, that are useful in the
judgment of temperature and texture of various foods.
Mouth (cont.)
Tongue
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The tongue nearly fills the mouth when closed. Mucous membranes cover
the tongue. A membranous fold called the frenulum connects the midline of
the tongue to the top of the mouth
Tongue is also useful because it has the ability of moving food underneath
the teeth for chewing.
The tongue consists of rough projections called papillae on the surface of
the tongue which provides friction, which helps handle the food.
Papillae also bare taste buds
The roof of the tongue is also known as the posterior region, it is anchored
to the hyoid bone
Posterior region is covered with round masses of lymphatic tissue these are
called lingual tonsils
Mouth (cont.)
Palate:
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Forms the roof of the oral cavity, and consist of a hard anterior (hard
palate) part and a soft posterior (soft palate) part
Soft palate forms a muscular arch which extends posteriorly and
downwards as a cone shaped projection called the uvula
While swallowing the soft palate and uvula draw upward to prevent food
from entering the nasal cavity
Palatine tonsils are masses of lymphatic tissue on either side of the tongue
that are closely associated with the palate
The palatine tonsils lie beneath the epithelial lining of the mouth they
protect against infection
The Pharyngeal tonsils or adenoids are above the border of the soft palate
on the posterior wall of the pharynx.
Mouth (cont.)
Teeth
 There are two different sets of
teeth during development
primary and secondary teeth
 Primary teeth erupt through the
gums between the ages of six
months to 2 years old.
 The secondary teeth usually
appear around the age of six
years old
Salivary glands
The salivary glands secrete saliva.
 Saliva moistens food particles helping to bind them so they can start the
process of chemical digestion of carbohydrates.
 Saliva is a solvent
 Saliva dissolves foods so that they can be tasted and it helps cleanse the
mouth and teeth
 With in each salivary gland there are two types of secretory cells the
Serous cell and the Mucous cell
 Serous cells produce watery fluid the contains amylase, this enzyme splits
starch and glycogen molecules into disaccharides which is the first step of
the chemical digestion of carbohydrates.
 Mucous cells secretes a thick liquid called mucous this liquid binds food
particles and lubricates during swallowing.
Salivary Glands (cont.)
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The three major parts of the Salivary Glands are the parotid,
submandibular, and sublingual glands
Parotid Glands : are the largest of the major Salivary glands each of these
glands lies anterior to the ear between the cheek and the masseter muscle.
The parotid glands secrete a clear fluid that is rich in amylase.
Submandibular Glands: are located in the floor of the mouth on the inside
surface of the lower jaw. The secretory cells of the these glands are
predominantly serous, containing a few mucous cells. Submandibular
glands secrete a viscous fluid than the parotid.
Sublingual Glands: is the smallest of the salivary glands are on the floor of
the mouth inferior to the tongue. Secretary cells are primarily the mucous
type making their secretions thick and stringy.
Pharynx and Esophagus
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Pharynx connects to the nasal and oral cavities with the larynx and
esophagus. There are three different parts.
Nasopharynx: communicates with the nasal cavity and provides a
passageway for air during breathing
Oropharynx: is posterior to the soft palate and the inferior to the
nasopharynx. It is a passageway for food moving downward from the
mouth and for air moving to and from the nasal cavity.
Laryngopharynx: just inferior to the orophaynx is a passage to the
esophagus.
There are three stages of swallowing.
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Food is mixed with the saliva and forced into the pharynx
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Involuntary reflex actions move the food into the esophagus
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Peristalsis transports food to the stomach
Pharynx and Esophagus
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Esophagus is a a straight,
collapsible tube about 25
centimeters long, is a food
passageway from the pharynx
to the stomach
 The esophagus begins at the
bottom of the pharynx and
goes down the posterior to the
trachea, that passes through the
the mediastinum.
 Circular muscle fibers at the
distal end of the esophagus
that helps prevent regurgitation
of food from the stomach
Stomach
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The stomach receives food, mixes it with gastric juice carries on a limited
amount of absorption and moves food into the small intestine.
Parts of the stomach
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The stomach is divided into cardiac, fundic, body, and small intestine
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The cardiac regions is a small area near the esophageal opening
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The fundic region which balloons superior to the cardiac portion is a
temporary storage area
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Main part of the stomach lines between the fundic and pyloric portions
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Pyloric region narrows and becomes the pyloric canal as it approaches
the small intestine. At the end of the pyloric canal, the muscular wall
thickens, forming a powerful circular muscle, the pyloric sphincter.
This muscle is a valve that controls gastric emptying
Stomach (cont.)
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Regulation of Gastric Secretion: gastric glands secrete gastric juice.
Gastric juice contains pepsin. This begins the chemical digestion of
protein hydrochioricacid and intrinsic factor.
The regulation of gastric secretions is the parasympathetic impulses
and the hormone gastrin that enhances gastric secretion.
Food in the small intestine reflexly inhibits gastric secretions
Gastric Absorption: when the stomach absorbs a few substances,
such as water and other small molecules
Mixing and Emptying Actions: after a meal the mixing movement of
the stomach wall acid in producing a semi fluid paste of food
particles and gastric juice called chyme.
Peristaltic waves push the chyme closer to the pyloric sphincter then
the muscles begin to relax, during stomach contractions chyme is
pushed little by little into the small intestine
Stomach (cont.)
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The rate of which the stomach
empties depends upon the
fluidity of the chyme and the
type of food present
 When liquids are passed
through the stomach, it is
moved along rapidly.
 Whereas solids stay until they
are well mixed with gastric
juice
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Fatty foods will stay in the
stomach for three to six
hours
Foods high in proteins move
through more quickly
Carbohydrates pass through
faster than fats and proteins
Pancreas
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The pancreas also has an exocrine function - secretion of a digestive juice
called pancreatic juice
The pancreas is closely associated with small intestine. It is located
horizontally across the posterior abdominal wall in the C-shaped of the
duodenum
Pancreatic juice contains enzymes that can split carbohydrates, fats, nucleic
acids, and proteins. Pancreatic juice has a high bicarbonate ion
concentration that helps neutralize chyme and causes intestinal contents to
be alkaline
Hormones regulate pancreatic secretion
Secretin stimulates the release of pancreatic juice with a high bicarbonate
ion concentration
Cholecystokinin stimulates the release of pancreatic juice with a high
concentration of digestive enzymes
Liver
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The liver is located in the upper right quadrant of the abdominal
cavity, just inferior to the diaphragm
The right and left lobes of the liver consist of hepatic lobules, the
functional units of the gland. Biles canals carry the bile from hepatic
ducts
The liver mobilizes carbohydrates, lipids, and proteins; stores some
substances it filters blood, destroys toxins and secretes bile.
The only liver secretion there is is bile that also directly affects
digestion.
The liver plays a specific part in carbohydrate metabolism by
maintaining the normal concentration of blood glucose. Liver cells
that are responding to hormones such as insulin and glucagons lower
the blood glucose level by breaking down glycogen or by converting
noncarbohydrates into glucose
Liver (cont.)
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Most vital liver functions concern protein metabolism. This includes
deaminating amino acids forming urea, synthesizing plasma proteins
(clotting factors) and converting certain amino acids to other amino
acids
The liver also stores glycogen, iron, and vitamins A, D, and B12
Macrophages in the liver help destroy damaged red blood cells and
phagocytize foreign antigens. The liver also removes alcohol from
the blood and secretes bile
Bile contains bile salt, bile pigments, cholesterol, and electrolytes.
Only the bile salts have digestive functions
The gallbladder is a pear-shaped sac located in a depression on the
livers inferior surface. Its attached to the cystic duct which in turn
joins the common hepatic duct.
Liver (cont.)
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The gallbladder is lined with
epithelial calls and has a strong,
muscular layer in the wall that
stores bile between meals,
reabsorbs water to concentrate
bile, and contracts to release bile
into the small intestine
A sphincter muscle controls the
release of bile from the common
bile duct
The sphincter muscle at the base
of the common bile duct relaxes
as a peristaltic wave in the
duodenal wall approaches
Small Intestine
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The small intestine is a tubular organ that extends from the pyloric
sphincter to the beginning of the large intestine, with its many loops and
coils it fills much of the pancreas and liver
It completes digestion of the nutrients in chyme, absorbs the products of
digestion and transports the residues to the large intestine
The small intestine consists of of three portions: the duodenum, the
jejunum, and the ileum
The duodenum is 25 centimeters long and 5 centimeters in diameter, lies
posterior to the parietal peritoneum and is the most fixed portion of the
small intestine
The proximal two filths of this portion is the jejunum and the remainder is
the ileum
A double-layered fold of peritoneal membrane called mesentery suspends
these portions from the posterior abdominal wall
Small Intestine Diagram
Small Intestine (cont.)
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The wall is lined with villi that greatly increase the surface area and aid in
mixing and absorption
Secretions from the small intestine include mucus and digestive enzymes.
Digestive enzymes split molecules of sugars, proteins, and fats into simpler
forms
Mechanical and chemical stimulation from chyme causes goblet cells to
secrete mucus. Distention of the intestinal wall stimulates parasympathetic
reflexes that stimulate secretions from the small intestine
Enzymes in microvilli perform the final steps in digestion. Villi absorb
monosaccharides, amino acids, fatty acids and glycerol.
Monosaccharide are absorbed by the villi through active transport or
facilitated diffusion and enter blood capillaries
Small Intestine (cont.)
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Amino acids are absorbed into the villi by active
transport and are carried away in the blood
 Fatty acids are absorbed and transported differently
than the other nutrients
 The small intestine carries on segmentation and
peristaltic waves
 The ileocecal sphincter at the junction of the small
and large intestines usually remains closed unless a
gastroileal reflex is elicited after a meal.
Large Intestine
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The large intestine absorbs water and electrolytes and forms and
stores feces
The large intestine consists of the cecum, colon, the rectum, and the
anal canal.
The anal canal opens to the outside as the anus; it is guarded by an
involuntary internal anal sphincter and a voluntary external anal
sphincter muscle
The large intestinal wall has the same four layers found in other
areas of the alimentary canal, but lacks many of the features of the
small intestinal mucosa such as villi
Fibers of longitudinal muscle are arranged in teniae coli that extend
the entire length of the colon, creating a series of pouches
Large Intestine (cont.)
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The large intestine does NOT digest
or absorb nutrients, but it does
secrete mucus; absorbs electrolytes
and water; and contains important
bacteria that synthesize vitamins
and use cellulose.
 Peristaltic waves happen only two
or three times during the day in the
large intestine
 Defecation is stimulated by a
defecation reflex that forces feces
into the rectum where they can be
expelled.
 Feces are composed of undigested
material, water, electrolytes, mucus,
and bacteria. Both the color of feces
and its odor is due to the action of
bacteria
Nutrition and Nutrients
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Nutrition is the process by which the body takes in and uses nutrients
Essential nutrients are those that cannot be synthesized by human cells
Carbohydrates, such as sugars and starches, are organic compounds used
for sources of energy in the diet.
Carbohydrates can be consumed in a variety of ways: starch from grains,
glycogen from meat, and disaccharide and monosaccharide sugars from
fruits and vegetables.
Complex carbohydrates are broken down into monosaccharides
Monosaccharides that are absorbed in the small intestine are fructose,
galactose, and glucose; the liver converts the first two into glucose
Excess glucose is stored as glycogen in the liver then converted into fat and
stored adipose tissue
The need for carbohydrates varies with a person's energy requirements; the
minimum requirement is unknown
Nutrition and Nutrients
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Lipids are organic substances that supply energy for cellular processes and
to build structures.
Lipids include fats, phospholipids, and cholesterol
Most common of lips are triglycerides. Triglycerides are found in plantand animal-based foods.
Digestion breaks down triglycerides into fatty acids and glycerol.
A normally based human diet varies widely in lipid content. A typical diet
consisting of a variety of foods usually provides adequate fats
Proteins are polymers of amino acids. Foods rich in protein include meats,
fish, poultry, cheese, nuts, eggs, and cereal.
Legumes include beans and peas, contain lesser amounts
Cells in an adult can synthesize all but eight required amino acids, whereas
children can produce all but ten
Nutrition and Nutrients
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Amino acids that the body
can synthesize are
considered nonessential,
whereas those that
cannot are essential
amino acids
This refers to only to
dietary intake since all
amino acids are required
for normal protein
synthesize
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A protein called
gliadin in wheat is an
example of partially
complete protein
which does not
contain enough lysine
to promote growth,
but contains enough
to maintain life.
Nutrition and Nutrients
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Vitamins are classified in two different basis of solubility, one that involves
fats and the other with water
Fat-soluble vitamins: this includes vitamins A, D, E, and K. These are
carried in lipids and are influenced by the same factors that affect lipid
absorption
Water-soluble vitamins: this includes vitamins B, and C. B vitamins make
up a group and oxidize carbohydrates, lipids, and proteins. C vitamins is
the least stable, and widespread in plant foods, and is necessary for
collagen production
Minerals are elements other than carbon that are essential in human
metabolism. Plants usually extract minerals from soil, and humans obtain
minerals from plant foods or from animals that have eaten plants
Adequate Diets
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An adequate diet is based upon sufficient energy, essential
fatty acids, essential amino acids, vitamins, and minerals that
will support optimal growth and maintain and repair body
tissues.
Because an adequate diet requirements are greatly dependent
upon age, sex, growth rate, amount of physical activity, and
level of stress, designing a diet adequate for everyone is
impossible
Because of this a Department of Agriculture in the U.S has
created a series of food pyramids based upon age, medical
conditions, ethnicity, food preferences, vegetarianism, and
weight loss goals.
Food Pyramid
Adequate Diets
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There are highly different diets for someone who
is a normally active person compared to someone
who is athlete such as a weight lifter.
 Someone who lifts weights on a regular basis
would stick to a high protein low carb diet.
 For example a normally active person would
endure around 50 grams of protein a day whereas
a weight lifter would consume around 100 grams
Diseases/Disorders
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Appendicitis: Is caused by, in some cases, when small objects block the
opening. Which then creates bacteria that grows and causes and infection.
It is most common in people 10-30. Symptom is belly pain, pain can
become severe while moving coughing or walking.
Crohn’s Disease: Caused by inflammation of the digestive (or
gastrointestinal) tract. 500,000 people are affected in the U.S which tends
to run in families. Symptoms are upset stomach, bouts of diarrehea, and
bowel obstruction. Treatments are eating helthy, regular exercise,
medications, nutritional supplementation, and surgery.
Colitis: Is inflammation of the colon leaving sores, or ulcers, on the inside
lining that can bring on frequent bouts of diarreha and abdominal cramps.
Usually occurs between the ages of 15 and 30. Possible causes are genetics,
environmental factors, and immune system responses.
Works Cited Page
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http://okinawa-diet.com/okinawa_diet/food_pyramid.html
http://glencoe.mcgrawhill.com/sites/0218378151/student_view0/chapter15/textbook_images.html
http://glencoe.mcgrawhill.com/sites/0218378151/student_view0/chapter15/study_outline.html
http://www.everydayhealth.com/health-center/appendicitis.aspx
http://www.everydayhealth.com/crohns-disease/index.aspx
http://www.everydayhealth.com/ulcerative-colitis/ulcerative-colitiscauses.aspx
Shier, David. Hole’s Essentials of Human
Anatomy and
Physiology. Boston: Mc Graw Hill Higher Education. 2006. 386-420.
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